Highly flexible instrument for medical applications

ABSTRACT

A highly flexible instrument particularly useful in medical applications is elongated and formed of a plurality of flexible metallic strands, at least one strand being spirally wound and having a scraping edge thereon.

CROSS-REFERENCE

This is a continuation application of U.S. application Ser. No.09/469,553, now U.S. Pat. No. 6,267,592 entitled, A HIGHLY FLEXIBLEINSTRUMENT FOR MEDICAL AND/OR DENTAL APPLICATIONS filed Dec. 22, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a highly flexible instrument that isparticularly adaptable for use as an endodontic instrument, mostparticularly, an endodontic file for use by practitioners in removingthe pulpal material from an exposed root of a tooth and for shaping theroot canal to receive filler material, usually gutta-percha. One of themost significant advancements in dentistry in recent years has beenimproved treatment of abscessed teeth. In the past a tooth, onceabscessed, was usually pulled as the only remedy for removing theintense pain usually created when a tooth is abscessed. By “abscessed”usually means that the root canal of the tooth becomes infected and theinfection causes pressure on the tooth and the nerve endings associatedtherewith that result in sometimes almost unbearable pain. With theadvent of endodontics the drastic measure of extracting a tooth that hasbecome abscessed has been eliminated.

The first step in the endodontic treatment of an abscessed tooth is todrill an opening in the crown of the tooth to provide access to the rootcanal. Once the root canal adjacent the crown is exposed, thepractitioner then must thoroughly clean the root canal of pulpalmaterial since if the pulpal material is not thoroughly and carefullyremoved it can be the source of continued infection within the interiorof the tooth. Not only is it necessary that the pulpal material be cleanbut the root canal usually must be shaped in such a way as to permitcareful filling of the root canal with a filler material. While othertypes of filler materials have been provided still at the present timethe most common filler is a paste-like material referred to as“gutta-percha.” If the canal is not properly cleaned and shaped the stepof filling with gutta-percha may leave void areas that invite theintroduction into the root canal of organic matter that can be followedby bacterial action. For these reasons much of the effort by apractitioner to successfully accomplish the endodontic treatment of anabscessed tooth is the cleaning and shaping of the root canal and thesesteps are accomplished utilizing small diameter tapered files that areinserted by the practitioner through the exposed crown area into theroot canal. The canal must be cleaned from the crownal area advancing tothe root apex. Root canals naturally occur in a tapered configuration,that is the cross-sectional diameter of the root canal is usuallygreater near the crown of the tooth and usually is at a minimum at theapex of the tooth, that is the distal end of the root of the tooth.While the root canal is naturally tapered it is not taperedsymmetrically and the canal can have inclusions in intermediate portionsbetween the apex and the crown area that interfere with the passage offiller material. Therefore the crown must be shaped to removeunnecessary intrusions into the canal and to improve the chances thatthe practitioner can successfully fill the root canal with fillermaterial.

Files are usually provided with a small cylindrical plastic handleportion by which the practitioner manually manipulates the files. By“manipulation” means inserting a file into a canal and reciprocating itto file away intrusions and at the same time to gather pulpal materialand the results of the scraping action. Typically the practitionerinserts a file to the point of resistance and then rotates andreciprocates the file to engage spiral scraping edges with the canalwall and then extract the file to remove pulpal material and matterscraped from the wall. This procedure is repeated as necessary to cleanthe entire length of the canal. In the cleaning process the practitionerusually starts with a file of a small diameter and then, as progress ismade in cleaning the canal, larger diameter files are employed until theroot canal is shaped and cleaned to the apex. Accordingly, endodonticfiles usually come in sets of standard tapers and varying from small tolarger diameters.

Root canals are characteristically not straight. Some root canals curvemore than others but few are perfectly straight from the crown to theapex. Therefore it is important that files be flexible so as to be ableto follow the natural curvature of the root canal as it is cleaned andshaped from the tooth crown to the tooth apex. If a file is too stiff itcan result in the file protruding through a side wall of the root whichcan introduce an area of infection into the tooth and therefore ishighly undesirable. Further, if the file is stiff it is less successfulin cleaning the entire area of a canal since the stiffness will causethe file to be deflected drastically to one side of a curve in a canalleaving a portion of the wall that defines the inside of the curveunexposed to the action of the file for cleaning and shaping. Therefore,a high degree of flexibility is a very desirable characteristic of anendodontic file.

In addition, the strength of a file is very important. In the process ofreciprocating and rotating a file in a tooth it is possible for the fileto break off leaving a broken part in the tooth. This creates a seriousproblem for the practitioner. Accordingly, it has long been a desire ofthe dental profession to have available dental files that are highlyflexible and yet strong to resist separation as a result of a torsionaltwist or pulling action as a file is manipulated within a root canal.The present invention provides a way of substantially increasing theflexibility of dental files while at the same time increasing resistanceagainst torsional or elongational separation.

2. Prior Art

For additional background information on the construction and use ofhighly flexible instruments, such as endodontic files, reference can behad to the following previously issued United States patents includingthe references cited in each of them.

U.S. PAT. NO. INVENTOR TITLE 4,934,934 Arpaio, Jr. et al. DentalFile/Reamer Instrument 5,106,298 Heath et al. Endodontic DentalInstrument 5,628,674 Heath et al. Endodontic Instrument

SUMMARY OF THE INVENTION

A highly flexible instrument for medical and/or dental applications hasan elongated metallic body formed of a plurality of flexible metallicstrands. One application of the invention is an endodontic file in whichthe instrument has a scraping edge thereon. The scraping edge can beformed by employing at least one metallic strand that is non-circular inconfiguration, such as triangular. A spiraled scraping edge ispreferably achieved by winding a non-circular cross-sectional strand onthe outer surface of a plurality of base strands. The invention can bepracticed by employing one or more central strands, surrounded by aspirally wound strand that is non-circular in cross-section providing aspiraled scraping edge. Another embodiment employs one or more centralstrands surrounding by a first spirally wound strand and on top of it asecond strand spirally wound in the opposite direction. The outermostspiraled strand is non-circular to provide a scraping edge.

A better and more complete understanding of the invention will beobtained from the following description of the preferred embodimentshaving reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational isometric view, highly enlarged, of anelongated metal strand that is tapered from a proximal end towards adistal end and is non-circular in cross-section. FIG. 1 is pentagonal asan illustration of one non-circular cross-sectional embodiment.

FIG. 2 is an isometric elevational view of three of the strands of FIG.1 assembled together.

FIG. 3 is a view of the three strands of FIG. 2 wherein the workingportion of the file has been twisted to form a spiral externalconfiguration that provides three interleaved spiral scraping edges.

FIG. 4 is a cross-sectional view of one configuration of a file bodyformed of three pentagonal strands as taken along the line 4—4 of FIG.3.

FIG. 5 is a cross-sectional view of an alternate embodiment showingthree strands each having a hexagonal shape.

FIG. 6 shows in cross-section four strands each having a triangularconfiguration fitted together to form a square.

FIG. 7 is an alternate embodiment of FIG. 6 showing a cross-sectionalview of four strands, each of triangular cross-sectional configuration,but wherein the strands are of different sizes.

FIG. 8 is a cross-sectional view showing three triangular strandstogether to form a file body wherein the overall body is triangularproviding three scraping edges.

FIG. 9 shows four strands, each of triangular configuration, assembledso that the cross-section of the file body is triangular providing threescraping edges.

FIG. 10 shows the arrangement wherein four strands having squarecross-sections are assembled together to form a file body that is squarein cross-section.

FIG. 11 is an elevational view of the first stage of manufacturing amulti-strand endodontic file showing a single base strand and a handlefor manual manipulation.

FIG. 12 is an elevational view of a file employing the apparatus of FIG.11 in which an elongated strand is wound on the center strand and inwhich the elongated strand is of triangular cross-section. Theembodiment illustrated in FIGS. 11 and 12 provides a tapered file inwhich the outer spirally wound strand is not required to be tapered andprovides a file that does not require machining after assembly.

FIG. 13 is a cross-sectional view taken along the line 13—13 of FIG. 12.

FIG. 14 is an elevational view of a file in which a tapered centerstrand that is circular in cross-section is wound first in one spiraldirection with a smaller diameter strand that is non-tapered and iscircular in cross-section followed by a spirally wound strand on theouter surface that is triangular in cross-section.

FIG. 15 is a cross-sectional view taken along line 15—15 of FIG. 14.

FIG. 16 shows a file having a handle portion configured to be receivedin a hand piece by which the file can be rotated. The file of FIG. 12includes three central elongated tapered strands surrounded by a singlespiral wound strand having a triangular cross-sectional shape to formscraping edges on the exterior surface.

FIG. 17 is a cross-sectional view taken along line 17—17 of FIG. 16showing three central strands that are tapered and are of circularcross-sectional configuration surrounded by a single strand that isspirally wound on the three circular strands, the spiraled wound strandbeing triangular in cross-section.

FIG. 18 is an alternate embodiment of a file of FIG. 16 having multiplecentral strands that are circular in cross-section surrounded by a firstspiral wound layer that is also circular in cross-section followed by anouter spiraled wound strand that is triangular in cross-section. Theouter spiral wound strand is wound in a direction opposite to the innerspiral wound layer.

FIG. 19 is a cross-sectional view taken along the line 19—19 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention described herein is a highly flexible instrument formedical and/or dental applications. One specific application of theinvention is as a highly flexible file useful in removing plaque fromveins and arteries and is particularly useful for removing pulpalmaterial from root canals. Such files are called “endodontic files” andthe invention will be described as it is used in endodontic fileapplications, however, this is not to be taken as a limitation on theapplication of the invention.

Endodontic files are used in two basic ways. In the most common way thefile has at its proximal end a small cylindrical handle, usually made ofplastic that is manipulated between the thumb and forefinger of thepractitioner. A practitioner inserts the file into a root canal andmanually reciprocates and rotates it to clean and shape the canal. Theother basic type of endodontic file is used in a hand piece—that is, ahandheld instrument that provides rotation like a drill. The file headportion is inserted into a chuck device in the hand piece and thepractitioner can control the rotation thereof as the file is moved intoand out of a root canal. FIGS. 11 through 14 show examples of files ofthe first type, that is wherein each file has a handle portion 10 formanual manipulation. FIGS. 16 and 19 are external views of files inwhich the handle portion 12 is configured to be received in the chuck ofa handpiece by which the file can be rotated as used by a practitioner.

Normally files come in sets of different diameters. A practitionernormally starts with a small diameter and as the root canal is cleanedand shaped switches gradually to larger diameters until the root canalis cleaned and shaped from the crown area down to the root apex and isin condition for receiving the application of filler material, such asgutta-percha. This invention provides an endodontic file that functionsin the same way and for the same purpose as endodontic files in presentuse but provides a file that has improved flexibility and resistanceagainst breakage. Essentially, improved flexibility is achieved byemploying the concept of utilizing a plurality of flexible metal strandsthat form the file body. This contrasts with files as used today whereinthe file body is a unitary metallic member usually basically cylindricalon its working surface and tapered from a proximal end to the distal endwith one or more spiral grooves providing spiral lands with scrapingedges that serve to scrape a root canal as the file is used.

FIG. 1 shows an example of a single flexible metallic strand 14 that canbe employed in the manufacture of an endodontic file. Strand 14 has aproximal end 16 and a distal end 18 and is non-circular incross-section. From the isometric external view of FIG. 1 it can be seenthat any cross-section taken perpendicular the length of strand 14 ispentagonal. This is by way of example only. In practicing the inventionthe file body or working portion is preferably formed of a plurality ofelongated metal strands and in one embodiment of the invention the metalstrands are non-circular in cross-section. FIG. 1 is an example of onetype of non-circular strand.

FIG. 2 is a diagrammatic view of an assembly of three elongated flexiblemetallic pentagonal strands 14 assembled together to form a first phasein the manufacture of the body of an endodontic file. FIG. 3 shows theassembly of FIG. 2 in which the working portion has been twistedproviding a plurality of spiral scraping edges. It can be seen in FIG. 4that the assembly of three pentagonal members provides six longitudinaledges indicated by 20A through 20F. When the working portion of the filebody is twisted as in FIG. 3 all of the edges 20A through 20F take aspiral pattern and provide interleaved spiral scraping edges. The filedistal end 18 of the assembly is tapered or pointed so that the filewill be guided as it follows a root canal of a tooth during anendodontic procedure.

The use of elongated strands having a pentagonal cross-section as shownin FIGS. 1 through 4 is exemplary of the concept of manufacturingendodontic files out of a plurality of strands in which the strands arenon-circular in cross-section so that when the multiple strands areassembled and twisted spiral scraping edges are provided without therequirement of machining the exterior surface of the file. If desirable,machining can be applied to the spiral wound assembly of FIG. 3 toreshape the scraping edges.

FIG. 5 is a cross-sectional view of an assembly of three elongatedstrands wherein each of the strands has a hexagonal configuration. Thisconfiguration provides, after the assembly is twisted as in FIG. 3,three scraping edges 22A, 22B and 22C showing that the number ofscraping edges varies according to the nature of the assembly.

FIGS. 6 through 10 show additional cross-sectional embodiments whereinthe file body portion is formed of a plurality of strands of differentcross-sectional configurations. For instance, FIG. 6 is a cross-sectionof an assembly of strands used in manufacturing an endodontic fileemploying four elongated strands 24A through 24D when the assembly ofFIG. 6 is twisted four interleaved spiraled scraping edges 26A through26D are formed.

FIG. 7 shows a different embodiment in cross-section in which fourtriangular strands are employed, that is 28A through 28D but in whichthe strands have two different cross-sectional shapes. Strands 28A and28C have triangular cross-sections equally dimensioned, that isgeometrically the same, while strands 28B and 28D are triangular but ofreduced dimensions. The assembly of FIG. 7 when twisted will provide anelongated shaft having four scraping edges 30A through 30D. Theconfiguration of FIG. 7 is considered superior to that of FIG. 6 sincein FIG. 7 the scraping edges 30A are formed at intersecting sides of thesame strand in each case instead of as in FIG. 6 wherein scraping edges26A-26D are formed at the intersection of two strands. Further, scrapingedges 30A-30D of FIG. 7 are defined by acute angles whereas in FIG. 6the scraping edges 26A-26D are defined by right angles.

The cross-sectional view of FIG. 8 shows the use of three triangularcross-sectioned strands 32A-32C that provide three edges 34A-34C.

FIG. 9 is a cross-sectional view of another assembly of elongatedstrands of non-circular cross-section providing an overall triangularcross-sectional arrangement wherein four strands 36A-36D are employed.Each of the strands is of the same cross-sectional triangular shapeassembled in a way so that the four strands provide three scraping edges38A-38C. When the assembly of FIG. 9 is twisted it provides a file shaftportion having three spirally wound scraping edges 38A-38C and whereineach of the spiral edges is at an acute angle and each edge is formedintegrally of the same strand. The arrangement of FIG. 9 is superior tothat of FIG. 8 for the same reason as explained in the comparison ofFIGS. 6 and 7—that is, in FIG. 9 the cutting edges 38A-38C areintegrally formed each by a single strand.

FIG. 10 is a cross-sectional view of four strands 40A-40D, each strandbeing of the same square cross-sectional shape. This assembly providesfour scraping edges 42A-42D when the assembly is twisted as in FIG. 3.

The examples of FIGS. 1 through 10 are illustrative of various ways inwhich the invention may be practiced wherein an endodontic file has ashaft formed of a plurality of elongated flexible tapered strands thatare spirally wound about each other to provide spiral scraping edges.

To prevent the plurality of tapered flexible metallic strands fromseparating from each other after being assembled together the distal endportion 18 as indicated in FIG. 3 can be treated to bond the strandstogether. This can be achieved by subjecting tip 18 to a fusingtemperature or solder may be applied to the tip end portion.Alternatively, a high strength epoxy may be employed to bond the strandsto each other at the tip 18.

Whereas known endodontic files in use today employ a solid unitaryelongated tapered metal shaft from the proximal to the distal portionthe endodontic file of this invention is different in that it employs aplurality of tapered flexible metallic strands to form the shaft of anendodontic file. There are two significant advantages achieved by theuse of a plurality of strands versus forming a file wherein the shaft isunitary. First, a plurality of strands provides significantly increasedflexibility compared to a single integral shaft body. The advantages offlexibility are easy to understand when the flexibility of multi-strandcopper wire is compared with a single solid copper wire having the samecurrent carrying capacity. The root canals of human teeth are typicallynot straight but are invariably curved as the canal extends from theroot apex to adjacent the tooth crown. For this reason it is importantthat endodontic files be flexible so as to follow the contour of a canalas a file is inserted into the canal.

In addition to flexibility it is also important that endodontic files beresistant to breakage, that is resistant to being severed byelongational pull or torsional twists. If a lower portion of a filebreaks off in a root canal it is considered a serious problem byendodontists and therefore every effort is made to prevent breakage of afile in the process of cleaning and shaping a root canal. Thus, thedesigners of endodontic files are forced into compromising betweenstrength and flexibility. Endodontic files are customarily made ofsteel, usually stainless steel. Stainless steel is in many ways an idealmetal for making a file since it is typically relatively strong comparedto other metals is relatively flexible and chemically resists reactionwith the pulpal material in a tooth. However, recent tests haveindicated that certain metal alloys improved flexibility withoutsignificant loss of elongation or torsional strength. A most prominentalloy having such improved flexibility is a combination of nickel andtitanium and is referred to in the trade as “Nitinol.” Comparisons madeof the relative advantages of stainless steel and Nitinol were publishedin an article entitled “An Initial Investigation of the Bending and theTorsional Properties of Nitinol Root Canal Files”, Journal ofEndodontics, Vol. 14, No. 7, July, 1988 at pages 346-351. The advantagesof the endodontic file of this invention that improve flexibility by theuse of a plurality of metal strands are enhanced when the metal strandsare formed of a high flexibility, high strength alloy such asnickel-titanium or Nitinol. Nitinol typically consists of about 40%titanium and 60% nickel although the exact percentages of the alloy canvary. One disadvantage in the use of nickel-titanium appears that theprocess of grinding cutting surfaces on a tapered shaft made of Nitinolfrequently results in the cutting surfaces having ragged edges such ascaused by metal deposits as a result of the grinding operation. In theinvention herein where a plurality of flexible tapered metal strands ofnon-cross-sectional configuration are employed, the scraping edges areformed without the necessity of further machining after the file isformed thus eliminating a problem which has existed in some types ofpreviously known endodontic files manufactured with nickel-titaniumshafts.

FIGS. 11 through 15 show alternate embodiments of the invention. Thefirst embodiment is shown in FIGS. 11, 12 and 13. FIG. 11 shows anelongated unitary metallic shaft 44 that is tapered from a proximal end46 to a pointed distal end 48. The upper portion of the proximal end 46of shaft 44 is encompassed within a plastic formed handle portion 10 aspreviously described. The shaft 44 of FIG. 13 is round in cross-sectionhowever it could be of other cross-sectional arrangements.

Spirally wrapped about shaft 44 is a metallic strand 50 having anon-circular cross section, in this case a triangular cross-section asseen in FIG. 12. The spirally wound strand provides a spiral scrapingedge 52 that extends from the shaft proximal portion 46 to distal end48. It should be noted in comparing FIGS. 11, 12 and 13 that the baseshaft 44 is tapered in the way that endodontic files are typicallytapered however the spiral wound strand 50 does not have to be tapered.This is one embodiment by which the invention of FIGS. 11, 12 and 13 maybe practiced. Spirally wound strand 50 could be tapered, having asmaller cross-sectional size as the strand approaches file distal end 48(not shown).

FIG. 11 and the cross-sectional view of FIG. 15 show shaft 44 as beingof circular cross section and unitary that is, a single base shaftextends from the distal to the proximal end. It is understood thatinstead of a unitary shaft 44, a tapered central shaft can be formedusing a plurality of individual tapered strands such as the taperedstrands of FIG. 2 wherein the strands can have a variety ofcross-sectional configurations.

The advantage of the endodontic file of FIGS. 11 through 13 is that thecentral shaft 44, whether unitary or made up of a plurality of taperedstrands, can be of a relatively smaller diameter since the ultimateoperating diameter of the file is achieved by spirally wound strand 50,thus providing a file shaft body of smaller cross-sectional area andtherefore greater flexibility. Further, the spirally wound strand 50provides a cutting edge and adds torsional strength withoutsignificantly adding to the rigidity of the file. Thus the advantages ofthe embodiment of FIGS. 11 through 13 are increased flexibility and inaddition, the provision of a file having a spiraled scraping edgewherein no machining work is required to be done on the assembled fileshaft.

The end of spirally wound strand 50 at distal end 48 is preferablysecured to the shaft such as by spot welding, solder, epoxy bonding orotherwise and the same is true at the upper end of the spirally woundstrand 50 at the base shaft proximal end 46. In addition, the spirallywound strand 50 can be attached at other places along the length ofshaft 44 such as by the use of laser welding as a way of ensuring asecure relationship between inner shaft 44 and spirally wound shaft 50without significantly detracting from the high flexibility of the totalassembly.

FIGS. 14 and 15 show an alternate embodiment employing the basicsubstructure of the file as shown in FIGS. 11 through 13, that is a filewith an elongated shaft 44 that may be unitary as illustrated. In theembodiment of FIGS. 14 and 15 the elongated tapered central shaft 44 hasa first spirally wound small diameter strand 54 that, as shown in FIG.15, may be circular in cross-section. The small diameter strand 54 iswound helically on shaft 44 from the proximal end 14 adjacent handle 10down to adjacent the distal end 44. A second outer spiraled strand 56 isthen helically wound on top of the inner spirally wound strand 54. Theouter spiraled strand 56 is preferably wound in the opposite directionof the inner spirally wound strand 54. The end portions of innerspirally wound strand 54 are secured to base shaft 54 at the oppositeends thereof such as by welding, soldering, braising, adhesive, etc. Inlike manner the outer spirally wound strand 56 is secured to theassembly by welding, soldering, braising, adhesive, etc. The secondsmall size outer spiraled strand 56 is non-circular in cross-section,such as triangular as shown in FIGS. 14 and 15 to provide a spiraledscraping edge 58.

The advantages of the arrangement of FIGS. 14 and 16 having a doublespiral wrapping around the base shaft as compared to the single spiraledwrapping of FIGS. 12 and 13 is that in the embodiment of FIGS. 14 and 16the resistance to torsional separation of the file is substantiallyincreased. This is so since rotation of the shaft proximal end relativeto the distal end in either clockwise or counter-clockwise directionwill result in applying tension to either the inner spirally woundstrand 54 or the outer spirally wound strand 56. Therefore, theembodiment of FIGS. 14 and 15 achieve an endodontic file having a highdegree of flexibility and resistance to torsional separation and thescraping edge does not need to be machined on to the file body as withexisting types of files.

FIGS. 16 and 17 show an embodiment that is like FIGS. 12 and 13 withonly two changes. In FIGS. 16 and 17 handle 12 is configured to bereceived in a handpiece as has been previously described. Further, thecentral shaft of the file of FIGS. 16 and 17 is formed of a plurality ofelongated tapered shaft portions 60A-60C. The use of three strands toform the central shaft of the file is only exemplary as the shaft can bemade with any number of strands. In the arrangement of FIGS. 16 and 17the tapered central strands 60A and 60C may be straight, that is theyneed not necessarily be twisted around each other although this could bedone. Further, the central strands 60A-60C are shown to be circular incross-section although they could be of other cross-sectionalconfigurations.

Wrapped around the plurality of central tapered strands 60A-60C is aspirally wound strand 62 that, in the illustrated arrangement, is ofuniform dimension from end to end although, as previously explained, itcould be tapered. Economy of manufacture obviously suggests the use of anon-tapered strand 62. The strand is non-circular cross-sectionalconfiguration such as a triangle as illustrated in FIG. 17 providing aspiral scraping edge 64.

The final illustrated embodiment is shown in FIGS. 18 and 19 and isdifferent from the embodiment of FIGS. 14 and 15 in two ways, that is bythe use of a handle portion 12 intended for insertion into a dentalhandpiece and wherein the central shaft is formed of a plurality ofelongated tapered metallic strands 60A-60C as has been described withreference to FIGS. 16 and 17. Wrapped around the elongated taperedcentral strand 60A-60C is a first spirally wound small diameter innerstrand 66 which, as was explained with reference to FIG. 15, may beeither circular or non-circular in cross-sectional configuration.Spirally wound inner strand 66 may be of uniform external diameteralthough optionally it could be of tapered diameter.

Helically wound on the exterior of inner strand 66 is outer strand 68,the outer strand being wound in an opposite helically direction frominner strand 60. The strands are secured at their ends to the centralshaft strand 60A-60C and at spaced apart intermediate points if desired.Outer strand 68, when triangular in cross-section as shown, provides aspiral scraping edge 70. The inner and outer spirals obtained by innerstrand 66 and outer strand 68 have advantages as previously indicated,that is resistance to torsional breakage while at the same timemaintaining high flexibility.

It needs to be pointed out that the drawings herein are notdimensionally representative of endodontic files but are illustrative ofthe principles by which flexible files of this invention may bemanufactured. The typical endodontic file has a shaft that extends froma handle not more than approximately three centimeters and the typicalendodontic file including the handle portion itself is typicallyapproximately four centimeters in length. The sizes illustrated hereinare grossly enlarged.

The embodiments of FIGS. 11 through 19 are particularly adaptable to theuse of nickel-titanium alloy in their manufacture for the reasonspreviously described. Further, in the embodiments herein wherein aplurality of strands are employed the alloy of which the strands aremade can be mixed, that is not all of the strands in any configurationneed to be of the same alloy. As an example, in the embodiments of FIGS.11 and 12 the main shaft 44 may be of nickel-titanium alloy whereas thespirally wound strands 50 in FIG. 12 or 54 and 56 of FIG. 14 may bestainless steel or some other alloy, the reason being that the smalldimensions of the spirally wound strands lend themselves to inherentlystiffer material without dramatically increasing the overall stiffnessof the finished endodontic file.

The claims and the specification describe the invention presented andthe terms that are employed in the claims draw their meaning from theuse of such terms in the specification. The same terms employed in theprior art may be broader in meaning than specifically employed herein.Whenever there is a question between the broader definition of suchterms used in the prior art and the more specific use of the termsherein; the more specific meaning is meant.

Whereas, the present invention has been described in relation to thedrawings attached hereto, it should be understood that other and furthermodifications, apart from those shown or suggested herein, may be madewithin the spirit and scope of this invention.

What is claimed is:
 1. A highly flexible instrument for medicalapplications comprising; an elongated instrument body formed of aplurality of elongated flexible metallic strands including at least onecentral strand that is tapered in cross-section from a larger dimensionadjacent said body proximal end to a smaller dimension adjacent saidbody distal end, said at least one central strand being surrounded by atleast one spirally wound strand having at least a portion that isnon-circular in cross-section.
 2. An instrument according to claim 1wherein said body has a proximal end and a distal end, and including ahandle portion at said proximal end.
 3. An instrument according to claim2 wherein said handle portion is configured for engagement by amechanically rotated chuck.
 4. An instrument according to claim 2wherein said handle portion is configured for manual manipulation.
 5. Aninstrument according to claim 1 wherein at least some of said pluralityof elongated flexible metallic strands are twisted about each other andwherein said scraping edge is formed by the cross-sectional shape of oneof said metallic strands.
 6. An instrument according to claim 1 whereinat least one of said strands has at least a portion that is at leastsubstantially triangular in cross-section.
 7. An instrument according toclaim 1 wherein at least one of said strands has a portion that ispentagonal in cross-sections.
 8. An instrument according to claim 1wherein at least one of said strands has a portion that is hexagonal incross-sections.
 9. An instrument according to claim 1 wherein saidstrands are bonded to each other at a body distal end.
 10. An instrumentaccording to claim 1 wherein at least some of said strands are twistedabout each other.
 11. A highly flexible instrument for medicalapplications according to claim 1 wherein said at least one spirallywound strand that is non-circular in cross-section provides at least onescraping edge.
 12. A highly flexible medical instrument having a freeend comprising: an elongated tapered body having a proximal end and areduced diameter distal end and formed of a plurality of elongatedflexible metallic strands extending from adjacent said proximal end toadjacent said distal end, —one of said strands being a central strandtapered in cross-section from a larger dimension adjacent said proximalend to a smallest dimension adjacent said distal end surrounded by—atleast one—spirally wound—strand having at least one scraping edge. 13.An instrument according to claim 12 wherein said body is uniformlytapered from said proximal end to said distal end.
 14. An instrumentaccording to claim 13 including a handle portion at said body proximalend.
 15. An instrument according to claim 12 wherein said body has ahandle portion at said proximal end.
 16. An instrument according toclaim 15 wherein said handle portion is configured for engagement by amechanically rotated chuck.
 17. An instrument according to claim 15wherein said handle portion is configured for manual manipulation. 18.An instrument according to claim 12 wherein said scraping edge isspiraled.
 19. An instrument according to claim 12 wherein at least someof said plurality of elongated flexible metallic strands are twistedabout each other and wherein said scraping edge is formed by thecross-sectional shape of one of said metallic strands.
 20. An instrumentaccording to claim 12 wherein at least one of said strands has at leasta portion that is at least substantially triangular in cross-section.21. An instrument according to claim 12 wherein at least one of saidstrands has a portion that is pentagonal in cross-sections.
 22. Aninstrument according to claim 12 wherein at least one of said strandshas a portion that is hexagonal in cross-sections.
 23. An instrumentaccording to claim 12 wherein said at least one center strand issubstantially straight with respect to at least one other strand.
 24. Aninstrument according to claim 12 wherein said strands are bonded to eachother at a body distal end.
 25. An instrument according to claim 24wherein said strands are bonded to each other at said body distal end byfusion.
 26. An instrument according to claim 12 wherein at least some ofsaid strands are twisted about each other.